This paper reviews current genetic and molecular biological methods that may be used in the so-called "reverse genetics" approach. These methods are the mapping, isolation, and study of the chromosomal DNA containing a previously unidentified gene responsible for a genetic disease, beginning with its chromosomal localization. In principle, the reverse genetics methodology follows the same path for different diseases studied. An overall outline of the steps to be undertaken is given and discussed. Several stages are illustrated with reference to current research in the fields of Duchenne muscular dystrophy, Huntington's disease, and polycystic kidney disease.